Biggest Loser contestants 'drop like flies' as they try to scale 10,000 steps at the Sydney Opera House

TWO Biggest Loser competitors 'dropped like flies' after collapsing while scaling 10,000 stairs during a task called 'The Punisher' at the Sydney Opera House.

Challenged by what former Olympian Hayley Lewis dubbed 'The Punisher' last night, visibly struggled, vomiting along the way as they battled the landmark building.

The youngest, Caitlin, 17, had earlier revealed she used to get bullied at school, dropping out before the end of Year 12, and that this had drive her on to compete.

'I used to get called a hefer, a pig, a whale, fat, a slob. When the Biggest Loser came to Ararat, I knew I had to do this,' she said.

All too much ... Caitlin hits the deck.Source:Supplied

Out for the count ... It's all too much for Ca...Source:Supplied

C'mon, you can ...Source:Supplied

Enough to make you sick.....Caitlin tries to get her breath.Source:Supplied

Help at hand ... An assistant comes to Caitlin'...Source:Supplied

Apprehensive ... Mary appeared terrified of the task.Source:Supplied

Got for it.....Cal takes to the stepsSource:Supplied

But despite, but in the end it was all too much, and she promptly threw up after she and fellow competitor Matt completed 6192 steps.

Trainer Shannan Ponton reassured her it was just due to drinking too much water, Caitlin had a rest before resuming the stairs.

'To her credit, she got up and got back into the race,' Shannan said.

But it wasn't too long before she was back on the ground again and being treated by medics on site.

Not long after her teammate Matt did exactly the same, but with Caitlin completely out, he was forced to get back up and do the lion share of the work.

And the duo were not the only ones falling ill from the challenge.

Natalie also fell to the ground under strain.

With her and partner Craig behind in the bottom two, the couple suffered a blow when she came to her knees after feeling light headed.

'When I got to the top of the stairs I was already beginning to feel a bit dizzy. My head started to spin and I sort of felt myself going down,' she explained.

Struggle...Shannon.Source:Supplied

Ironically Shannon, the lightest contestant, struggled the most.

The young mother admitted that her bad self confidence stopped her from doing many things in life and she mostly stayed indoors.

'I fear everything. I fear of dying. I fear of heights... Deep down I feel empty. I don't feel like I do anything of importance,' said Shannon as a flashback showed her looking at herself in a mirror while wearing her underwear.